Process for preparation of 1h-imidazo-(4,5-b)pyrazin-2-ones

ABSTRACT

A PROCESS IS DESCRIBED FOR THE PREPARATION OF 5-AMINO(OR SUBSTITUTED AMINO) - 6 - CHLORO - 1H - IMIDAZO(4,5-B)PYRAZIN-2-ONES WHICH COMPRISES HEATING A 3 - AMINO - 5AMINO (OR SUBSTITUTED AMINO)-6-CHLOROPYRAZINOYLAMINIMIDE EITHER IN A SUITABLE SOLVENT OR AS A SOLID UNTIL REARRANGEMENT AND RING CLOSURE IS COMPLETE. THE PRODUCTS HAVE UTILITY AS ANTIHYPERTENSIVE AGENTS.

United States Patent 3,567,725 PROCESS FOR PREPARATION OF IH-IMIDAZO- [4,5-b]PYRAZlN-2-ONES Edward J. J. Grabowski, Iselin, Edward W. Tristram, Cranford, and Roger J. Tull, Metuchen, N.J., assignors to Merck & Co., Inc., Rahway, NJ. N0 Drawing. Filed Nov. 20, 1968, Ser. No. 777,478 Int. Cl. C07d 51/76 US. Cl. 260-250 20 Claims ABSTRACT OF THE DISCLOSURE A process is described for the preparation of S-amino- (or substituted amino) e 6 chloro-lH-i-midazo[4,5-b]- pyrazin-Z-ones which comprises heating a 3 amino-- amino(or substituted amino)-6-chloropyrazinoylaminimide either in a suitable solvent or as a solid until rearrangement and ring closure is complete. The products have utility as antihypertensive agents.

This invention relates to a novel process for the preparation of lH-imidazo[4,5-b]pyrazin 2-ones from novel derivatives of 3-aminopyrazinoic acids. In particular it relates to the novel process of preparing S-amino- (or substituted amino)-6-chloro-1H imidazo[4,5-b]pyrazin-2- ones from novel (3-amino-5-amino(or substituted amino- 6-chloropyrazinoyl) aminimides. The process is represented by the following equation:

II 0 0H wherein R represents 1) hydrogen,

( 2) lower cycloalkyl of from 3 to about 7 carbon atoms, e.g., cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl and the like,

(3) mononuclear aryl, especially phenyl,

(4) amidino, substituted with lower alkyl, or lower alkylcarbonyl,

(5) lower alkynyl of from 3 to about 5 carbon atoms such as propargyl,

(6) lower alkenyl of from 3 to about 5 carbon atoms,

such as allyl,

(7) lower alkyl of from 1 to about 6 carbon atoms either straight or branched chain such as methyl, ethyl, propyl,

3,567,725 Patented Mar. 2, 1971 wherein R represents (1) hydrogen,

(2) lower alkyl of from 1 to about 5 carbon atoms, e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, pentyl, isopentyl, neopentyl and the like,

(3) lower alkylcarbonyl, of from 2 to about 3 carbon atoms, e.g., acetyl, propionyl, and the like;

R represents (1) hydrogen,

(2) lower alkyl, of from 1 to about 5 carbon atoms, e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, pentyl, isopentyl, neopentyl, and the like;

R and R when lower alkyl can be linked to gether either directly or through a hetero atom such as nitrogen or oxygen to form a heterocycle with the nitrogen to which they are attached, e.g., piperidino, pyrrolidinyl, morpholino, piperazinyl, N-lower alkylpiperazinyl, and

the like;

R represents hydrogen or lower alkyl of 1 to about 3 carbon atoms such as methyl, ethyl and propyl;

R and R when lower alkyl can be linked together either directly or through a hetero atom such as nitrogen or oxygen to form a heterocycle with the nitrogen atom to which they are attached forming, e.g., piperidino, pyrrolidinyl, morpholino, piperazinyl, N-lower alkylpiperazinyl, and the like;

R represents lower alkyl of 1 to about 3 carbon atoms such as methyl, ethyl and propyl;

R is hydrogen or lower alkyl of 1 to about 6 carbons.

The novel process of this invention comprises heating the novel starting material of Formula I, either neat, in solution, or in suspension in a diluent which causes a rearrangement and ring closure to the product II. The reaction is best conducted in an inert organic solvent for I with a boiling point greater than about C., such as Xylene, Z-methoxyethanol, or diethylene glycol dimethyl ether, ethanol, pyridine, scollidine, dimethylformamide, dimethylsulfoxide, p-chlorobenzene, toluene, 1,l,2,2-tetrachloroethane, 1,1,2,2-tetrachloroethylene, or the like, by heating the solution to a temperature between about 75 C. and the melting point of the paricular solute for from 0.5 to about hours followed by cooling, and quenching into an inert solvent such as water or n-hexane, if neces sary, which causes precipitation of the product II. Although the reaction is best conducted in solution as described above, comparable results, as suggested, are also obtained by heating compound I to its melting point until fusion is complete, or by suspending the starting material in an organic liquid with a boiling point above the melting point of the starting compound, and heating the suspension until reaction is complete.

The products of the process of this invention are orally active, relatively non-toxic, highly effective antihypertensive agents with a moderate degree of diuretic and saluretic activities. They can be administered in the form of pills, tablets, capsules, elixirs, injectable preparations, and the like, in compositions which comprise one or more of the compounds of Formula II as the only active ingredient or in combination with other therapeutic ingredients. The compounds are advantageously administered at a dosage range of from about 5 mg. per day to about 750 mg. per day per 70 kg. of body weight. The dosage can be given in subdivided amounts on a twofour time a day regimen.

Compounds of Formula II are tautomeric in nature and exist as lH-imidazo[4,5-b]pyrazin-2-ones (the structure shown in Formula II) and as the corresponding lH-imidazo[4,5-b]pyrazin-2-ols (the structures shown by Formulae 11a and 11b) as follows:

N \N /N 3 =0 f I H III) The aminimines of Formula V are prepared by treating an alkylene oxide of Formula III, wherein R is hydro gen or a C alkyl group, with a 1,l-di(lower alkyl) hydrazine, represented by Formula IV, wherein R is a C alkyl group. The reaction is conducted by dissolving the two reagents in approximately equimolar proportions (a slight excess of III is advantageous) in a polar solvent such as a lower alkanol, e.g., methanol, ethanol or propanol. The reaction can be conducted at any temperature between about ice-bath temperature and about ambient temperature, over a period of from about 10 to about 24 hours. The product V is normally not isolated, but is instead treated directly with the pyrazinoic acid ester of Formula VIII as described below.

The intermediate esters of Formula VIII are prepared by treating methyl 3-amino-5,6-dichloropyrazinoate (VI), with an amine of structure VII in a lower alkanol at reflux temperature. Cooling the reaction mixture causes the product VIII to crystallize from solution.

Treatment of the reaction mixture containing the aminimine (V) prepared as described above, with approximately an equimolar amount of the ester (VIII), and heating the resulting solution to about 65 C. to C. for from about 16 hours to about 48 hours results in the formation of the aminimide of structure I, which can be isolated by evaporation of the solvent.

The following preparations and examples illustrate the preparation of the intermediates and the process of this invention respectively. It is to be understood that they are examples only and are not intended to define the limits of substituents and/0r reaction conditions of the invention, but rather the limits extend to reasonable variations recognized by those skilled in the art.

(A) Preparation of methyl 3-amino-S-substituted-amino- 6-chloropyrazinoates Preparation A-l: Methyl 3-amino-5-ethylamino-6- chloropyrazinoate-A suspension of methyl 3-amino-5,6- dichloropyrazinoate (178 g., 0.8 mole) in 2-propanol 1.1 liters) is stirred while ethylamine (4.4 moles) in 2-propanol (2 liters) is added, and the mixture is refluxed for an hour. The product that separates on cooling is collected by filtration and dried. The yield is 89%. After recrystallization from 2-propanol, the methyl 3-amino-5- ethylamino-6-chloropyrazinoate melts at 149150 C.

Analysis.Ca1cd. for C H ClN O (percent): C, 41.66; H, 4.81; N, 24.29. Found (percent): C, 42.11; H, 5.05; N, 24.24.

By employing substantially the same method as in Preparation A-l, but substituting for the ethylamine, equimolar quantities of the amines identified in Table I, there is obtained the corresponding methyl 3-amino-5 substituted-amino-6-chloropyrazinoates also identified in Table I according to the equation therein.

TAB LE I 1 N R N 01 4 NH; N 4 NHz NH COOCH R R2 (1 COUCH (Equation I) 3 1 3 C 1- N N Product Analysis Calculated Found 51.1 R R 0. Formula C H N O H N Preparation A- CHECCH2 168-9 0911 0119402 44. 92 3. 77 23. 44. 82 3. 73 23. 99 A-3 CHaOOHzOH2.-- 142-44 CgHtsNrOsCl 41. 47 5. 03 21.49 41.56 5. 03 21.38

A-4 190-191 Cl2Hi2C1N502 49. 97 4. 12 23 49. 39 4. 06 23. 88

A- OH H 170-71 Ci3H12N502C1 49. 97 4. 12 23. 85 49. 36 4. 18 23. 61

208-10 01011141950301 41. 75 4. 90 24. 34 42. 64 4. 85 24. 69 125-7 C12H20N502C1 47. 76 6. 68 23. 21 47. 95 6. 31 23. 45 189-182 CnHwNaOaCl 43. 78 5. 44. 21 5. O7 114-16 C12H20N502C1 47. 76 6. 68 23. 21 47. 88 6. 63 23. 13 174 (160. C13H12ClN503.2HC1 38. 58 5. 98 17. 31 38. 97 5. 88 17. 12 108-09 C11H18N502C1 45. 91 6. 30 24. 34 46. 30 6. 26 24. 43 179-171 Ci2H2oC1N502HCl 42. 61 6. 2O 42. 5. 67

121-22 CmHmNsOzCl 48. 08 6. 95 23. 37 48. 31 6. 4O 23. 76 2)2 A-14 H 148-49 CuHzaNsOgCl 49. 05 6. 76 24. 52 48. 95 6. 64 24.

CHaN N (CH2) 3- A-15 H 158-69 C1aH20N503C1 47. 34 6. 11 21. 24 47. 41 6. O4 21. 17

O N (CH 3-- 11-16 CHa(CH2)2 CH3- 83-5 CiuHi5N4C1Oz 46. 42 5. 84 21. 46. 5 5. 75 21. 70 A-17 H HZ HF 3 175-178 0911131940301 41. 47 5. ()3 21. 49 41. 99 5. 18 21. 21

11-18 C2115 143-45 CrzHrsNsOzCl 48 23 47. 6. 11 23. 19

CH2CH2N-CH2CH2 A-19 'CH2CH20CH2CH2 197-8 CioH13N4O3C1 44. 04 4. 80 20. 44. 32 4. 74 20. 67

CH H 157-158 C17HzsC1N50a (maleate) 47. 28 6. 07 16. 22 47. 43 6. 06 16. 52

nC'4 a A-21 (CH3)2N(OH2)3 CHs- 292-203 C12H2 C1N5O2(HC1) 42. 61 6. 26 20. 71 42. 6. 09 21. 02 A.22 (C2H)2N (CH2)2- CH3- 51-54 CmHzzClNaOz 49. 44 7. 02 22. 18 49. 65 6. 67 22. 30

A-23 -N (CH3)2 293-204 CuHnClNeOz 43. 93 5 69 27. 94 43 5. 54 28. 17

A-24 (3-NHC 0 CH3 H 246-248 C9H11C1N003 37. 70 3. 87 29. 32 37. 43 4. 15 29. 0

A-25 C 0 CH3 11 175-179 CnHmClNaOa (B) Preparation of 1,1-di(1ower alkyl)-1-(2-hydroxylower alkyl)-2-(3-amino-S-substituted-amino-6-ch1oropyrazinoyl) aminimides Preparation B-l 1,1-dimethyl-1- (Z-hydroxypropyl) -2- (3-amino-5-ethylamino-6-chloropyrazinoyl -aminimide. A solution of 18 g. (0.31 mole) of propylene oxide in 200 ml. of methanol is cooled to 2 C. and 15 g. (0.25 mole) of 1,1-dimethylhydrazine in 50 ml. of methanol is added over a two minute period. The reaction temperature rises to 7 C. and then decreases to 2 C. The solution is allowed to Warm spontaneously to ambient temperature over 16 hours.

To the reaction solution is added 46.1 g. (0.20 mole) of methyl 3-amin0-5-ethylamino-6-chloropyrazinoate and the reaction solution is refluxed for 24 hours. The methanol is removed at reduced pressure and the residue is triturated with 150 ml. of isopropanol. The resulting precipitate is filtered, washed with 2X 50 ml. of isopropanol and dried to afford 49.4 g. (0.157 mole, 79%) of 1,1-dimethyl-1- (Z-hydroxypropyl) -2-(3-amino-5-ethylamino-6-chloropyrazinoyl)aminimide, M.P. 173-175 C. (dec.).

Analysis.-Calcd for C H ClN O (percent): C, 45.5; H, 6.7; N, 286.5. Found (percent): C. 45.2; H, 6.8; N, 26.5.

TABLE III-Contlnued K N N 5 /N NH: Ra /N 2 i 0 C1 CNN-CH CHR C1 N u 9 el N X 0 R H H Aminimide from M.P.- preparation R R R R C.)

34 B-34 t-C4Hn H CH3- CH;; 235

35 B-35 I H CH3- 0113- 256-257 36 B36 H0 (CH2)2 H CHa CH3- 250-251 37 B-37 H CH3- H 270-271 Cl CH2- 38 13-38 H CH;; CHa- 291-293 39 18-39 (CHyJzN (CH2): H CH3 CH 219-220 40 B-40 Q H CH3- CH3' 257 41 13-41 C2H5-- CH3 CH CH3- 203-205 42 B-42 (CH2)s CHa CH; 229

43 B-43 2)2 2)2 CHa- H 275 FORMULATION 1 35 FORMULATION 3 Dry filled capsule containing mg. of active ingredient per capsule S-ethylamine 6 chloro-1H-imidazo[4,5-b]pyrazin- 2-one 50 Lactose 275 Mixed powders 325 F0 RMULATION 2 [Inhalation aerosol containing 0.1 mg. of 5-ethylamino-6-ehloro-1H- imidazo[4,5-b]-pyraz1n-2ones] Per Per 150 cont-alner, containers, gram grams Procedure: A concentrate containing 3 gm. S-ethylamino-6-chloro-lH-imidazo[4,5-b]pyrazin-2-one and 79.5 gm. Freon 11 (trichlorofiuoromethane) in a 250 ml. capacity plastic coated bottle containing approximately 100 gm. of 6 mm. glass beads is roller milled for 48 hours to reduce the drug to a particle size of less than 10 A sufficient quantity of the milled concentrate (0.55 gm.) cooled to an appropriate temperature is transferred to each of the pre-cooled containers. The required amount of Freon 12/114 (dichlorodifiuoromethane/1,2- dichloro-l,1,2,2-tetrafluoroethane) is added and the container is sealed under pressure with a metering valve fitted with a plastic actuator and mouthpiece.

[Inhalation aerosol containing 0.5 mg. of 5-ethylamino-6-cl1loro-1H- imidazo[4,5-b]pyrazin-2 one] Procedure: The drug is dispersed in the Freon 11 (trichlorofluoromethane), milled to the desired particle size in the manner described in Formulation 2 and subdivided into the individual containers. Sufiicient Freon 12/ 114 (dichlorodifluoromethane/1.2 dichloro 1,1,2,2. tetrafluoroethane) is added to each container. The ascorbic acid dissolved in the anhydrous ethanol is likewise subdivided into individual containers. All operations are performed at an appropriately chosen temperature. Finally, the containers are sealed in the manner described in Formulation 2. Dosage forms containing from 0.2 to 1.0 mg. of active ingredient per spray can be prepared in a manner identical to that described above.

While the invention has been described with particular reference to certain variables in the process conditions and compound substituents, it is to be understood that the invention embraces related processes and substituents which are obvious extensions of those disclosed.

What is claimed is:

1. A process for the preparation of 5-NR R -6-chloroimidazo[4,5-b]pyrazin-2-ones of structure 13 wherein R is a member selected from the group consisting of hydrogen,

C -7 cycloalkyl,

phenyl,

lower alkyl-amidino,

lower alkylcarbonyl-amidino,

lower alkynyl,

lower alkenyl,

lower alkyl,

(9) hydroxy-lower alkyl,

(10) lower (alkoxy-alkyl),

( 1 1) pyridyl-lo wer alkyl,

(12) phenyl-lower alkyl,

(13) halophenyllower alkyl,

( 14) amino-lower alkyl wherein the amino group is of structure wherein R is a member selected from the group consisting of (a) hydrogen, (b) lower alkyl, lower alkylcarbonyl, and R is a member selected from the group consisting of (a) hydrogen, and (b) lower alkyl, and wherein R and R when lower alkyl can be linked together to form a saturated 5-6 membered heterocycle containing at least 1 nitrogen atom and up to 1 other heteroatom selected from oxygen and nitrogen which when nitrogen can be substituted with lower alkyl; R is a member selected from the group consisting of (1) hydrogen, and (2) lower alkyl, and wherein R and R when lower alkyl can be linked together to form a saturated 5-6 membered heterocycle containing at least 1 nitrogen atom and up to 1 other heteroatom selected from oxygen and nitrogen which when nitrogen can be substituted with lower alkyl which comprises heating a compound of structural formula to between 75 C. and the melting point of Compound I, wherein R and R are as defined above, R is lower alkyl, and R is selected from hydrogen and lower alkyl.

2. The process as claimed in claim 1, wherein the reaction is conducted in an organic solvent for Compound I, having a boiling point above 78 C.

3. The process as claimed in claim 1, wherein the reaction is conducted neat.

4. The process as claimed in claim 1, wherein the reaction is conducted with Compound I in suspension in an organic liquid with a boiling point above the melting point of Compound I.

5. The process as claimed in claim 1, wherein R is lower alkyl, R is hydrogen, and IR and R are as defined in claim 1.

6. The process as claimed in claim 1, wherein R is lower alkyl, R is hydrogen, and each of R and R is methyl.

14 7. The process as claimed in claim 1, wherein R is Rs lower alkylN R is hydrogen, and R R R and R are as defined in claim 1.

8. The process as claimed in claim 1, wherein R is Rs lower alkyl-N R is hydrogen, each of R and R is methyl, and R and R are as defined in claim 1.

9. The process as claimed in claim 1, wherein R is R5 lower alky1N R is hydrogen, each of R and R is lower alkyl, and each of R and R is lower alkyl.

10. The process as claimed in claim 1 wherein R is lower a1kylN R is hydrogen, each of R and R is methyl, and each of R and R is lower alkyl.

11. A process for the preparation of 5-ethylamino-6- chloro-lH-imidazo[4,5-b1pyrazin-2-one of formula which comprises heating at from 75 C. to its melting point, 1,1-dimethyl- 1- Z-hydroxy propyl) -2- (3 -amino-5- ethylamino-6-chloropyrazinoyl)aminimide of structure N C H NH NH;

I (t mes 01- CNNCHzCH-CH:

N n 9 es 12. The compound of structural formula II 663 O OH 15 wherein R is a member selected from the group consisting of (a) hydrogen, (b) lower alkyl, (c) lower alkylcarbonyl, and R is a member selected from the group consisting of (a) hydrogen, and (b) lower alkyl, and wherein R and R when lower alkyl can be linked together to form a saturated 5-6 membered heterocycle containing at least 1 nitrogen atom and up to 1 other heteroatom selected from oxygen and nitrogen which when nitrogen can be substituted with lower alkyl; R is a member selected from the group consisting of (1) hydrogen, and (2) lower alkyl, and wherein R and R when lower alkyl can be linked together to form a saturated 5-6 membered heterocycle containing at least 1 nitrogen atom and up to 1 other heteroatom selected from oxygen and nitrogen which when nitrogen can be substituted with lower alkyl; R is lower alkyl; and R is a member selected from the group consisting of hydrogen and lower alkyl.

13. The compound as claimed in claim 12, wherein R is lower alkyl, R is hydrogen, and R and R are as defined in claim 1.

14. The compound as claimed in claim 12 wherein R is lower alkyl, R is hydrogen, and R and R are each methyl.

15. The compound as claimed in claim 12 wherein R R5 lower alkyl-N R is hydrogen, and R R R and R are as defined in claim 12.

16 16. The compound as claimed in claim 12, wherein R is R5 lower alkylN R is hydrogen, R and R are each methyl, and R and R are as defined in claim 12.

17. The compound as claimed in claim 12 wherein R is R6 lower alkyl-N R is hydrogen, R and R are each lower alkyl, and R and R are each lower alkyl.

18. The compound as claimed in claim 12 wherein R is R5 lower alkylN R is hydrogen, R and R are each methyl, and R and R are each lower alkyl.

19. 1,1-dimethyl 1 -(2 hydroxypropyl)-2-(3-amino- 5-ethylamino-6-chloropyrazinoyl)aminimide.

20. -1,1-dimethyl 1 (2 hydroxypropyl)-2-(3-amino- S-dimethylaminoethylamino 6 chloropyrazinoyl)aminimide.

References Cited UNITED STATES PATENTS NICHOLAS S. RIZZO, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent o- 3,5 7,7 5 Dated March 2, 97

Inventor) Edward J. J. Grabowski et al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' In column 5, under heading R Preparation A-2,

"CHEC-CH; should be CHECCH In column 5, under heading R Preparation A-l2, e)2 2)a-" Should be s)2 2)4- In Column 5, under heading R Pre aration A-ll, "(CH3 2NH-(CH2 3-" should read (CH32N"(CH2)3" In column 6 under heading Found, Preparation A-l'i,

"#139" should be ---4l.90---;

In column 6, line 59, '49. kg. should be +9.9g.

In column 6, line 6 "286. 5" should be ---26. 5-;

In column 8, under heading R Preparation B-13, "C5H1 should be CHS- In column 8, under heading R Preparation B-l t, "CH3'I should be C5H1l- In column 7, under heading R Preparation B-l7, HOCHQCHZ- should be added;

In Table III, in the heading bridging columns 9-10 and columns 11-12, R in formula on right side should H read \N/ and In column 13, line "C 7 cycloalkyl" should be --C cyc1oalkyl--.

Signed and sealed this 2nd day of November 1971.

(SEAL) fittest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pat 

